76 On the Alloys of Steel. [1822. 



which, being in close contact with the rest of the mass, form 

 voltaic combinations with it in a very active state : or, in the 

 third place, it may result from the iron being mechanically 

 divided by the platinum, so that its particles are more readily 

 attacked by the acid, analogous to the case of protosulphuret 

 of iron. 



Although we have not been able to prove by such experi- 

 ments, as may be considered strictly decisive, to which of these 

 causes the action is owing, or how much is due to any of them, 

 yet we do not hesitate to consider the second as almost en- 

 tirely, if not quite, the one that is active. The reasons which 

 induce us to suppose this to be the true cause of the action, 

 rather than any peculiar and previous arrangement of the par- 

 ticles of steel and platinum, or than the state of division of the 

 steel, are, that the two metals combine in every proportion we 

 have tried, and do not in any case exhibit evidences of a 

 separation between them, like those, for instance, which steel 

 and silver exhibit ; that when, instead of an acid, weaker 

 agents are used, the alloy does not seem to act with them as if 

 it were a series of infinitely minute voltaic combinations of steel 

 and platinum, but exactly as steel alone would do ; that the mass 

 does not render platinum wire more negative than steel, as it 

 probably in the third case would do ; that it does not rust 

 more rapidly in a damp atmosphere ; and that when placed in 

 saline solutions, as muriate of soda, &c., there is no action 

 takes place between them. In such cases it acts just like 

 steel ; and no agent that we have as yet tried, has produced 

 voltaic action that was not first able to set a portion of the 

 platinum free by dissolving out the iron. 



Other interesting phenomena exhibited by the action of acid 

 on these steels, are the differences produced when they are 

 hard and when soft. Mr. Daniel, in his interesting paper on 

 the mechanical structure of iron, published in the Journal of 

 Science, has remarked, that pieces of hard and soft steel being 

 placed in muriatic acid, the first required fivefold the time of 

 the latter to saturate the acid ; and that when its surface was 

 examined, it was covered with small cavities like worm-eaten 

 wood, and was compact and not at all striated, and that the 

 latter presented a fibrous and wavy texture. 



The properties of the platinum alloy have enabled us to 



